Hawfinch survey update: Mar-May 2016

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By Marcus Ward, 13 August 2016

Spring is one of the busiest periods for the New Forest Hawfinch survey, as March heralds the first consecutive roost count of the year. This is where where I attempt to count all of the known roosts at dawn on consecutive days, to get a snapshot of the number of Hawfinch using the known roosts. This year, due to work commitments and poor weather, I started on 10 March and only managed to get all 22 known roosts counted by 08 April.

Numbers were slightly down this spring, with 351 Hawfinch counted from 22 roosts (average of 15.9 per roost) compared to 367 from 19 roosts in spring 2015 (average of 19.3 per roost). There are a number of potential reasons for this slight decrease so it is perhaps unwise to speculate, but I suspect a significant factor would be the poor beech mast crop of autumn 2015. Late winter/early spring is known to be a period when natural food supplies in the forest become depleted; this can only be magnified following a poor seed crop.

 

Immature Hawfinch at Bolderwood photographed by Marcus; young birds readily give themselves away with their incessant high-pitched begging call. They can be picked out from flocks leaving the roost on call, a good way of qualitatively determining how successful the season has been.
Immature Hawfinch at Bolderwood photographed by Marcus; young birds readily give themselves away with their incessant high-pitched begging call. They can be picked out from flocks leaving the roost on call, a good way of qualitatively determining how successful the season has been.

 

Almost as soon as the consecutive roost count is complete, focus switches to the impending Hawfinch breeding season. In a normal year I would look at a number of widespread breeding locations, but this year I opted to concentrate on a central study area. My intention was to look at the correlation between numbers of Hawfinch in the studied roost, relative to breeding attempts in the vicinity. If a link between the two can be proven, we will then be able to evaluate the approximate breeding population in the New Forest based on roost counts, which are significantly easier to count than finding several hundred individual nests!

The Rhinefield area was selected as the main study area this year, centred on the well-known Blackwater Arboretum finch roost. I started looking for nests and territories from the last week of April, and pinned down the first nest on 30 April hidden in ivy on an oak. Hawfinch nest finding is a time-consuming business, so I recorded breeding attempts either when a nest was found or when a begging female being fed by a male was located (a sure sign that a nesting attempt is underway).

 

The main study area centred on the Blackwater Arboretum roost, with dotted lines delimiting radii of 0.5 km, 1 km and 1.5 km within which breeding territories were located.
The main study area centred on the Blackwater Arboretum roost, with dotted lines delimiting radii of 0.5 km, 1 km and 1.5 km within which breeding territories were located.

 

On 03 May I counted the Blackwater Hawfinch roost and recorded a total of 14 single birds, four pairs, and a group of five emerging from the roost between 0507 and 0550 hrs. This can be interpreted as 14 ‘off-duty’ males, presumably attending active nests, four pairs yet to commence nesting, and a group of five non-breeders (these birds hung around the roost for some time, showing no urgency to move on). From this we can estimate 18 breeding pairs and five non-breeding birds are associated with the roost.

Up to the end of the following week I managed to map a total of 16 breeding attempts within 1.5 km of the roost site, suggesting that most of the birds using the roost are breeding nearby. I counted the roost again on 16 May and recorded 12 singles, one pair, and a group of five, which again loitered for some time, suggesting that 12 off-duty males were using the roost together with a single pair and the regular non-breeding birds. The number of presumed breeding birds had dropped from 18 to 13 over the period of two weeks.

The results are encouraging, given this is a first attempt using this novel methodology, but it will have to be repeated at different locations over the next few years before we can confidently determine a link between the numbers of birds using the roost and the number of breeding attempts in the vicinity – but then, nothing to do with Hawfinch is quick and easy!

Unfortunately, as the season progressed it became clear that there was limited breeding success for our New Forest Hawfinches. Juvenile birds can often be quite conspicuous, especially in the roost from early June, but only small numbers have been recorded in roosts and at traditional crèche locations, suggesting that although not a total failure the season has been a tough one. This is hardly surprising given the cold/wet spring we have experienced this year, combined with the beech mast failure of autumn 2015, no doubt making it a challenging time for many woodland species.

 

Adult female Hawfinch sat on the nest, taken by Marcus in 2013. Click here https://youtu.be/9LvUG3LsLU0 for a short clip showing the male feeding the female at the nest; typical behaviour which is often difficult to view.
Adult female Hawfinch sat on the nest, taken by Marcus in 2013. Click here https://youtu.be/9LvUG3LsLU0 for a short clip showing the male feeding the female at the nest; typical behaviour which is often difficult to view.

 

As a final note, during spring this year, two bait stations were set up in the core study areas in an attempt to attract Hawfinch for colour ringing. The first Hawfinch to be caught and colour-ringed was in the Bolderwood area on 17 April, and by the time of writing a total 21 Hawfinch have been colour-ringed by Marcus; this project is already shedding light on the movements and behaviour of Hawfinch in the New Forest – more details to follow in the autumn!

 

Adult male Hawfinch, colour-ringed ‘Yellow AD’ ringed by Marcus at Bolderwood on 15 May. This individual was later observed attending a freshly fledged juvenile, together with a colour-ringed female ‘Yellow AF’.
Adult male Hawfinch, colour-ringed ‘Yellow AD’ ringed by Marcus at Bolderwood on 15 May. This individual was later observed attending a freshly fledged juvenile, together with a colour-ringed female ‘Yellow AF’.